1. Field of Invention
This invention relates to the art of filament winding as applied to highly reinforced, hollow tubular members of large size and to fabricating such bodies to have thick walls that are densely packed with filamentary materials in substantially void free and uniformly dispersed thermoset resin. This invention, more particularly, relates to an improved filament winding procedure that efficiently produces these structures to dimensionally precise specifications.
2. Prior Art
Filament winding is well known for producing shaped bodies having continuous filamentary materials as reinforcements thereof. Measures ordinarily undertaken with this technique, however, would appear inadequate for efficiently fabricating hollow, highly reinforced, large tubular structures of the type contemplated by this invention.
The structures of this invention have thick and dimensionally precise walls densely packed with filamentary materials in substantially void free and uniformly dispersed thermoset resin. Usual filament winding practice, for a number of reasons, might suggest that these structures should be prepared in a series of repeated winding and cure operations in order to preserve dimensional precision in their walls.
Thick walls of large, highly reinforced, tubular structures are prone to slumping or other distortions during the winding and cure operations. This tendency is more pronounced in these highly reinforced, large, tubular structures that are fabricated with significant axial reinforcement. Filamentary materials that are positioned relatively highly axially (i.e., positioned with respect to the center longitudinal axis of the structure at an angle of between about .+-.5.degree. and .+-.15.degree.) to obtain this axial reinforcement cannot grasp preceding layers of fiber nearly as well as those that are positioned relatively more circumferentially. Large, highly reinforced tubular structures with such thick walls also take longer to fabricate. Slumping or other such distortions are generally time dependant; the longer time for fabrication, accordingly, provides for further aggravation thereof.
Still other considerations associated with the task of fabricating tubular structures of the aforementioned character include providing a relatively uniformly dispersed and substantially void free thermoset resin matrix for the densely packed filamentary materials. Certain resins, for example, may migrate in the thick walls prior to, and during curing, causing resin rich and resin poor areas in the structure. Moreover, a very large volume of filamentary materials is required to be wound within relatively short periods of time in producing large structures. Still further, large tubular structures of dimensional precision require mandrels with significant axial strength for dimensional stability.